1. Field of the Invention
The present invention relates to a solid catalyst component for use in the polymerization of .alpha.-olefins, a catalyst system containing said solid catalyst component, a process for producing .alpha.-olefin polymers using said catalyst system and polymers obtained by said process. More particularly, the invention relates to a process for producing .alpha.-olefin polymers, particularly granular elastomers and granular thermoplastic elastomers, having a high bulk density and a low content of fine powder by the process of slurry polymerization, bulk polymerization, gas phase polymerization and the like by the use of a solid catalyst component having a high activity per one transition metal atom, wherein a procedure for the removal of the catalyst residue and amorphous polymer is unnecessary and the particle form of the solid catalyst component is controlled quite satisfactorily.
2. Description of the Prior Art
As is generally well known, the so-called Ziegler-Natta catalyst composed of a compound of a transition metal belonging to Group IV to VI of the periodic table and an organometallic compound of a metal belonging to Group I to III of the periodic table is used in the process for producing polymers of .alpha.-olefins such as propylene, butene-1, and the like.
Particularly in the industrial production of .alpha.-olefin polymers, the titanium trichloride catalyst is extensively used.
However, in the above-mentioned process, an amorphous polymer is formed as a by-product in addition to the industrially valuable highly stereospecific .alpha.-olefin polymer.
This amorphous polymer is poor in industrial utility and exercises a greatly adverse influence upon the mechanical properties of the .alpha.-olefin polymer when the latter is used in processed articles such as film, fiber and the like.
Further, the formation of the amorphous polymer is disadvantageous from the industrial point of view, too, in that it causes a loss in starting monomer and requires that a particular apparatus be provided for removing the amorphous polymer.
Accordingly, if the formation of the amorphous polymer can be eliminated or suppressed to a very slight quantity, it will bring about a great advantage.
On the other hand, the .alpha.-olefin polymers obtained by such polymerization processes contain a residual portion of catalyst, which causes various problems in the point of stability, processability, and so on. Thus it is necessary to provide a particular apparatus for the removal of the catalyst residue and for stabilization.
This disadvantage can be overcome if the catalyst has a high activity expressed by the weight of formed .alpha.-olefin polymer per unit weight of catalyst. If such a catalyst is used, the apparatus for removing the catalyst residue becomes unnecessary, which reduces the production cost of the .alpha.-olefin polymer.
Previously [Japanese Patent Application Kokai (Laid-Open) No. 61-287,904 (U.S. Pat. No. 4,672,050)], the present inventors found that a catalyst system composed of:
(1) a trivalent titanium compound-containing solid catalyst component obtainable by treating a solid product, which is obtained by reducing a titanium compound represented by general formula Ti(OR').sub.n X.sub.4-n (R' represents a hydrocarbon residue having 1 to 20 carbon atoms, X represents a halogen atom, and n represents a number satisfying 0&lt;n.ltoreq.4) with an organomagnesium compound in the presence of an organic silicon compound having an Si--O bond, with an ester compound and a mixture of an ether compound and titanium tetrachloride;
(2) an organoaluminum compound; and
(3) a silicon compound having Si--OR" bond (R" represents a hydrocarbon residue having 1 to 20 carbon atoms) exhibits high activity and a high specificity in the polymerization of .alpha.-olefins.
However, when a solid catalyst such as a Ziegler-Natta catalyst is put to use on an industrial scale, the form of the catalyst particle plays a very important role in controlling the bulk density of the polymer, the dimension of the polymer particle and its fluidity, and the above-mentioned invention was not yet satisfactory in the point of the particle form of the solid catalyst.
In the polymerization of ethylene, there have been published some attempts to improve the particle form by using a solid catalyst prepared by supporting a titanium-magnesium compound on silica gel [Japanese Patent Application Kokai (Laid-Open) Nos. 54-148,093 and 56-47,407 (U.S. Pat. No. 4,315,999)].
Further, the present inventors have also proposed a method for improving the properties of the particle by using a solid catalyst prepared by impregnating silica gel with a titanium-magnesium compound [Japanese Patent Application Kokai (Laid-Open) No. 62-256802]. Although the form of the particle can be greatly improved by these methods, the silica gel used as the carrier largely remains in the product, which causes fish-eyes in the films and deteriorates the quality of the product.
On the other hand, olefinic thermoplastic elastomers have hitherto been produced by firstly producing polypropylene or another olefin resin and an olefinic copolymer rubber such as ethylene-propylene rubber or the like separately, and then blending them together. As is well known, however, such a process is disadvantageous from the viewpoint of cost because olefin copolymer rubbers are generally produced by a solution polymerization process and the process for blending the olefinic copolymer rubber with an olefin resin requires high power and therefore a large quantity of energy.
On the other hand, the direct production of a thermoplastic elastomer by a two-step slurry polymerization process under specified conditions was proposed in Japanese Patent Application Kokai (Laid Open) Nos. 55-80,418 and 57-61,012 (U.S. Pat. No. 4,489,195). However, this process was also disadvantageous in that the ethylene-propylene random copolymer largely dissolved into solvent to enhance the system viscosity, which made the removal of polymerization heat quite difficult, promoted the adhesion between the polymer particles, and made it difficult to carry out the production process stably. As a method for solving this problem, carrying out a random copolymerization of ethylene and propylene at an extremely low temperature (below 30.degree. C.) was proposed. However, this method was also disadvantageous in that catalyst activity was low under these conditions and large-sized refrigerating equipment had to be used for removing the heat of polymerization, so that it was uneconomical.
Further, in Japanese Patent Application Kokai (Laid-Open) No. 59-105,008 (Canadian Patent 1,219,996), a process for producing a thermoplastic elastomer by a gas phase two-step polymerization was proposed. Although in this process an inorganic oxide such as silica gel was used as the carrier for the solid catalyst component to decrease the adhesive force of the polymer particle, the improving effect was still unsatisfactory.
Olefinic elastomers are generally produced by the solution polymerization process. The solution polymerization process requires many steps such as a step for recovering the unreacted monomer, a step for removing ashes, a step for stripping, etc. and the resulting polymer exists in the state of a solution, so that the system is highly viscous, difficult to stir and not easily controllable thermally, and therefore this process is quite disadvantageous from the viewpoint of production cost.
As a method for solving such problems, slurry polymerization of ethylene and propylene, i.e. their random copolymerization in liquefied propylene, was proposed in Japanese Patent Application Kokai (Laid-Open) No. 59-71,306. Although this process improves in productivity, this process has to be carried out at an extremely low temperature (below 40.degree. C.) and therefore involves various problems such as a decrease in catalyst activity, the necessity for large-sized refrigerating equipment for removing the polymerization heat, etc. which are disadvantageous industrially.
Further, the direct production of an olefinic elastomer by the gas phase polymerization was proposed in Japanese Patent Application Kokai (Laid-Open) No. 59-230,011 (Canadian Patent 1,219,400). However, in this process, a low polymerization temperature must be adopted and the monomer to be polymerized must be diluted with a very large amount of inert gas such as nitrogen or the like for the purpose of preventing the adhesion of polymer particles and stably carrying out the gas phase polymerization. Thus, this process is low in productivity and disadvantageous industrially.
Under the above-mentioned circumstances, the problem to be solved by the present invention, namely, an object of the present invention, is to provide a polymerization catalyst having so high a catalyst activity as to make the removal of catalyst residue and amorphous polymer unnecessary, a process for producing .alpha.-olefin polymers using said catalyst by which are obtained .alpha.-olefin polymers having a high bulk density and a low content of fine powder and containing no inorganic oxides such as silica gel which cause fish-eyes when the polymer is used as film, and polymers obtained by said process.
Further, another object of the present invention is to solve the above-mentioned problems in the prior arts and thereby to provide a process for producing a granular olefinic thermoplastic elastomer and a granular olefinic elastomer of excellent performances by a gas phase polymerization process. Further, yet another object of the present invention is to provide an olefinic granular thermoplastic elastomer and a granular elastomer obtainable by said polymerization process.
Ethylene-propylene rubbers and the like contain a large quantity of polymers having low crystallinity, and their polymer particles are highly adhesive in general. Accordingly, it is difficult to stably carry out a gas phase polymerization with these polymers.
As the gas phase polymerization reactor for .alpha.-olefins, stirring-mixing tank type reactor, fluidized bed type reactor, fluidized bed type reactor having stirrer, and the like have hitherto been proposed. As the adhesive force of the polymer particles increases in the stirring type reactors, extremely high power becomes required for achieving the desired stirring speed, and the design of such apparatuses is accompanied with remarkable difficulty. Further, in such a state, uniform mixing is difficult to achieve and high temperature regions come to remain in some localities; due to which a part of the polymer forms a bulky mass and thereby injures the stirrer and thermometer in the reactor and makes it difficult to withdraw the polymer particles from the reactor via pipings.
On the other hand, in reactors in which the unreacted monomer is polymerized in a fluidized state, there appears a tendency to slag which remarkably increases the quantity of polymer particles flying onto gas circulation line and causes deposition on lines and their clogging.
Further, in such a state, there is a problem that the difficulty in stirring results in the partial formation of a polymer mass.
Further, when the polymer particles have a high adhesive force, clogging readily takes place in the pipings for transporting the particles. Further, bridging takes place in the under part of the cyclone or in the hopper, which makes it difficult to withdraw the particles stably.
Thus, it has been quite difficult to actually produce a polymer containing a large quantity of polymer having low crystallinity by gas a phase polymerization process, in spite of the advantage of gas phase polymerization that it uses no solvent for dissolving the polymer having low crystallinity.
Further, in an improved gas phase polymerization process, the removal of catalyst residue is substantially omitted. Thus, the catalyst system used therein must be highly improved in polymerization activity.